Explanation:
Where is the Sun when you see a rainbow?
Behind you, of course.
But you can see both a rainbow and the Sun (far right)
side by side in this graceful panorama recorded on July 28.
The cloudy sunset view covers a full 360 degrees around
the horizon, composed using 20 individual images taken from an
observatory
on the outskirts of Potsdam, Germany.
The rainbow itself is produced by sunlight
internally
reflected in rain drops from the direction opposite the Sun
back
toward the observer.
As the sunlight passes through the drops,
from air to water and back to air again,
longer wavelengths (redder colors) are
refracted
or bent less than shorter wavelengths (bluer colors),
separating the sunlight into the colors of the rainbow.
This sharp picture captures the full, bright, primary rainbow arc as well
as more subtle effects.
You can see a partial, dimmer, secondary rainbow arc above and
left of the primary,
and faint arcs just inside the primary rainbow called
supernumerary
rainbows.